It is an old theory proposed by a handful of astronomers
and scientists over the years. A professor at U.S. Berkeley has recently breathed new life into it.

Because Planet Earth has a long history of mass extinction
of life about every 26 million years, scientists have long been trying to think of reasons why this happens.

The ideas have ranged from occasional strikes by major
asteroids to the passage of a mystery "Planet X" that causes a pole shift and generates just enough havoc to kill large numbers,
but not all life.

Richard A. Muller, a physicist at University of California, Berkeley, has dusted
off an old idea that is about as plausible as all the others, and he has a handful of fellow scientists considering it.

Called the Nemesis theory, it goes like this: our Sun
has a companion star, probably a dead dwarf, that swings in a very wide orbit that brings it close enough every so many hundred
thousand years to cause wholesale death and destruction on Earth.

For Muller, the idea came by chance in about 1983 while
discussing with colleagues the concept of another popular theory; that a large meteor impact wiped out the dinosaurs. But
if that was so, the scientists wondered, why would similar events occur at those regular intervals of 26 million years? What
might cause our planet to get bombarded with giant space rocks at those times but not others?

It was while pondering this question that Muller dreamed
up the idea of a solar companion. He named the object after the Greek goddess of retribution. As one writer stated, he thought
that was a fitting name for "a killer star that roamed stealthily between solar systems flicking comets at dinosaurs."

After working out the numbers and the plausibility with
his colleagues, Muller found that the idea looked so possible he published his theory in the journal Nature in 1984, and then
wrote a book.

Mueller suggests that the culprit may be a common red
dwarf star, one of some 3,000 that are visible through binoculars or a small telescope from Earth. He believes the Nemesis
orbit ranges from one to three light years away from the sun, but occasionally swings close, passing through the Oort Cloud,
a halo of comets and space dust surrounding our solar system from beyond Neptune.

It is during that close pass that Nemesis does its lethal
work.

The gravity of the passing star would scatter a storm
of primordial comets, dislodging them from their once-stable orbits after billions of years. Many would be pulled toward the
larger Sun by its gravity. And a handful of these giant bodies would crash into Earth.

The effect, of course, would hit the planet like a nuclear
assault from space, causing massive clouds of dust, nuclear winter, a possible polar shift, and consequently, the mass extinction
of life.

How plausible is Muller's idea?

The notion of companion stars is very common. Astronomers
believe more than half of all known stars are part of such a binary system, where two stars are thought to have formed at
the same time from a single cloud of gas and dust.

The interaction of binary stars is believed to involve
a gravitational dance around a common point in the solar system. The larger star, which in our case is the Sun, remains close
to the center of the system, while the smaller star orbits in a wide arch, but always returning to a point near the heart
of the system.

Muller's theory is just that, a theory that is yet to
be proven. And if he is right, the odds of a close passing of Nemesis anytime soon are extremely thin.

Or are they? The last major catastrophic event that took
the dinosaurs and an estimated 70 percent of all life on Earth, is estimated to have happened about 65 million years ago.
Perhaps a visit by the death star is long overdue.